Answer:
I would use a specialized or preformed matrix for the posterior sector.
Step-by-step explanation:
Losing a cusp is a much more critical situation, that is, there will be less tooth remnant and less resistance to functional and parafunctional forces.
The matrices that are usually used in the posterior sector are matrices that must be burnished and already come with a format to better restore the functional unit of the occlusal surface.
It is important to clarify that cusps are only in the posterior sector and not in the anterior sector.
The cusps, even if they have the most correct selection of the matrix, will fail in their restoration if they are not performed according to the patient's occlusion, under a good dental integration system such as adhesion through resins, and respecting the normal antomy of the piece to be restored.